content: /**
   * Provides the core classes for dataflow and actor programming.
   * Dataflow programming model has many flavors. 
   * This implementation has following features:
   * <p>
   * - computational dataflow graph is represented as tree of nodes
   * <p>
   * - nodes are created dynamically
   * <p>
   * - nodes have ports to accept and send tokens (messages and signals).
   * <p>
   * - the framework activates node after all the ports are unblocked:
   *  - input ports carry incoming tokens
   *  - output ports has memory to save output messages.
   *  There are no output ports for signals, as they do not require memory.
   * <p>
   * - nodes are executed by an executor set at the period of time between node creation and first execution.
   * If no executor is set, then {@link java.util.concurrent.ForkJoinPool} is used.
   * <p>
   * - nodes are subclasses of abstract class {@link org.df4j.core.actor.AsyncProc}.
   * <p>
   * - ports may be of several predefined types, and user can create specific pin types
   * by subclassing class {@link org.df4j.core.actor.AsyncProc.Port}.
   *
   */
  
  package org.df4j.core;